But full-time police national serviceman Muhammad Shazwan Sapuwan abused his authority and threatened a young couple to do his bidding.

Then a Special Constable Corporal, the 21-year-old wore his police warrant card to frighten the teenage couple after he caught and photographed them having sex on a staircase landing at a Housing Board block.

Threatening to take them to a police station, he told the couple he would let them go only if they let him record a video of the then 16-year-old girl performing oral sex on her boyfriend, also 16.

Even though the frightened couple complied, Shazwan proceeded to rape the girl while the boy looked on helplessly.

Yesterday, Shazwan, now 23, was sentenced to jail for 18 years and 15 strokes of the cane after pleading guilty to one count each of rape, sexual assault by penetration, outrage of modesty and extortion.

A second sexual assault by penetration charge involving the girl, one count of cheating and three other extortion charges were taken into consideration.

The court heard that Shazwan had other victims.

On separate occasions in 2014, he snuck up on two couples behaving intimately at HDB staircases and recorded them on video.

After introducing himself as a police officer, he cheated one of his victims out of $200 in August that year and extorted cash totalling $1,720 from another the following month.

The court heard that on Oct 24, 2014, Shazwan tailed the 16-year-old couple to a staircase landing and photographed them having sex.

Deputy Public Prosecutor (DPP) Sellakumaran Sellamuthoo said the girl had met her boyfriend after school at around 1.45pm that day and they went to a block of flats in the north-western part of Singapore.

They went to a staircase landing on the seventh storey where they got intimate and the girl performed oral sex on the boy.

FOLLOWED

Shazwan, who had followed the pair, spied on them from the eighth storey. He snapped two photographs of the couple.

When they were done, Shazwan came forward. He wore a lanyard displaying his police warrant card.

DPP Sellakumaran said he was also wearing a Jurong Police Division Headquarters polo T-shirt and a pair of blue police pants.

Shazwan took down the teenagers' particulars and told them they had committed an offence of "public nudity".

When the girl told him she did not want her parents to find out about the incident, he replied he would help the pair, but at the risk of losing his job. He then engaged them for about an hour for a solution.

As a bargain, Shazwan suggested filming them having sex. The boy was against the idea, but Shazwan insisted it was their only option. Out of fear, the couple eventually gave in.

While filming the teenagers, Shazwan decided to join in and forced the girl to perform oral sex on him.

He then raped her.

Shazwan left the scene once he was done, but told the couple to stay put.

At around 5pm, he called the boy to tell him they could go home.

But he was not done.

THREAT

Two days later, Shazwan contacted the boy and asked for $40. He threatened him with the sexually explicit videos.

The teenager complied and transferred the money over in two transactions.

Three days after her rape, the girl met her friends at school and started crying as she could not control herself any more.

DPP Sellakumaran said: "She disclosed the incident to her friends. Her friends managed to find the accused's identity through his Facebook profile and they encouraged her to make a police report.

"Later that day, the victim disclosed the matter to her family who then accompanied her to make a police report."

Shazwan was arrested hours later.

DPP Sellakumaran urged Judicial Commissioner (JC) Foo Chee Hock to sentence him to 18 years' jail with between 12 and 15 strokes of the cane.

He said: "Instead of upholding the law to protect life and property, the accused had lawlessly and brazenly abused his authority as a police officer to act to the detriment of those whose interests he was supposed to safeguard."

Before handing down the sentence, JC Foo said the sentence must be a deterrent one to "reflect society's abhorrence" of such offences.

Responding to queries from The New Paper, the Singapore Police Force (SPF) said: "Officers of SPF, including national service officers, are expected to uphold the law and set a good example by maintaining high standards of discipline and integrity.

"Those who commit offences will be charged in court and dealt with in accordance with the law."

For rape, Shazwan could have been jailed up to 20 years and fined or caned.

For extortion, he could have been jailed up to seven years and caned.

What can an officer with a warrant card do?

Police officers with warrant cards can ask members of the public they approach for their identification.

Former police officers The New Paper spoke to said the officers can also search them for items like dangerous weapons.

Mr Davy Chan, who was a policeman between 1967 and 1979, said that the officer can touch areas such as the person's waist or thighs.

He added: "But note that only a female officer can touch a woman.

"Officers are also not allowed to tell the people they approach to strip."

Mr Joseph Tan, who served in the police force from 1985 to 1992, said police officers tend to approach people whom they think appear suspicious.

Members of the public then have to cooperate with the officers.

Mr Tan, who founded the Crime Library, a voluntary group that helps track missing people, said: "If somebody does not have his ID with him, the officer may even accompany him or her home to obtain it.

"The officer can then exercise discretion on what to do next - whether to give a stern warning, let the person go or conduct an arrest if any offences were detected."